The present invention relates generally to a bearing assembly for rotating a shaft in a bearing sleeve. The invention relates in particular to a window for the output beam of a laser resonator in a hermetically sealed enclosure, the window being rotatable in the enclosure for placing different areas of the window in the path of the laser output.
It is common practice in the commercial laser manufacture to locate components of a laser resonator in a hermetically sealed enclosure for protecting the components from contamination by atmospheric gases and particulate matter. Typically, the output beam of an enclosed laser is delivered via a window that is provided in the enclosure. If the laser provides an output beam of high-energy radiation, such as ultraviolet radiation, the laser window may gradually be degraded by the radiation at an area of the window through which the laser radiation passes. This presents a problem, initially, in that it reduces the output power of the laser available outside the enclosure. Eventually, such degradation could require that the window be replaced to avoid further reduction of output power.
One arrangement for avoiding frequent replacement of a laser output window is to provide a window that has a much greater area, for example about 10 times the area or more, than the area through which the laser beam passes. When degradation of one area of the window becomes unacceptable, the window is moved such that the laser beam can pass through an undegraded area of the window. In order for this to be a practical solution to the output power degradation problem, the window must be easily movable, and preferably movable without breaking the hermetic seal of the enclosure, or contaminating the interior of the enclosure.
In a general aspect, the present invention is directed to a bearing assembly comprising a cylindrical bearing sleeve and a bearing shaft rotatably located in the bearing sleeve. The bearing sleeve has an inner wall including a circumferential groove extending therearound. The bearing shaft also has a circumferential groove extending therearound. The circumferential grooves are aligned with each other and a coil spring in the form of a continuous loop located within the grooves. The coil spring and the grooves are arranged such that the bearing shaft is rotatably and removably retained in the bearing sleeve.
Preferably the bearing sleeve and bearing shaft grooves are generally V-shaped and include first and second sloping surfaces. The coil spring is arranged to make point contact with the sloping surfaces of the grooves. Preferably, the coil spring is held under longitudinal tension in the bearing shaft groove with coils of the spring radially compressed between the grooves.
Particular aspect the present invention is directed to providing a rotatable window in an enclosure housing a laser. The cylindrical bearing sleeve is located in a wall of the enclosure. The bearing shaft is in the form of an open cylinder. The window is held within the open cylinder of the bearing shaft such that the window has a rotation axis corresponding to the rotation axis of the bearing shaft. The laser is arranged in the enclosure such that the output beam of the laser is transmitted through the window at a region thereon offset from the rotation axis thereof by a predetermined distance. The predetermined distance is selected such that the bearing shaft may be selectively rotated to cause the laser beam to be transmitted through the window at a second region thereon displaced from the first region. This arrangement permits that, should the laser window be damaged by the laser beam in one region, the window can be rotated such that the beam is transmitted through an undamaged region.
One advantage of the present invention is that the compression of the coil spring between the grooves provides a radial and longitudinal preload that combine to maintain the window in alignment as it is rotated. Another advantage of the bearing of the present invention is that the requirement for lubricants to facilitate rotation of the bearing is minimized. This makes it useful for providing a bearing access to an enclosure in which organic contaminants must be minimized.
It is emphasized here that usefulness of the inventive bearing assembly is not limited to the above-described window rotating application. Those skilled in the art may devise other applications for the bearing without departing from the spirit and scope of the present invention.